Thousands of firearms dealers along the U.S.-Mexico border now will be required to give the federal government the names of customers making multiple purchases of semi-automatic rifles favored by Mexican drug cartels, U.S. officials said Monday.

The federal Bureau of Alcohol, Tobacco, Firearms and Explosives said the new requirement in states bordering Mexico will provide valuable intelligence for derailing arms-trafficking rings that have thrived in Texas and elsewhere, and fed a war in Mexico that has taken at least 40,000 lives since late 2006.

Much like rules for handguns, dealers will have to send a form to the ATF within five business days whenever a person buys two or more of the targeted guns.

“The international expansion and increased violence of transnational criminal networks pose a significant threat to the United States,” said Deputy Attorney General James Cole, who announced the requirement.

It applies to guns that are greater than .22-caliber and use detachable ammunition clips, he said.

There are about 1,500 government-licensed firearms dealers in the Houston area — which the ATF contends is the No. 1 point of origin for guns recovered at cartel crime scenes in Mexico and traced back to where they were first sold – and 8,000 in Texas.

Many local gun dealers are adamantly opposed to the new rule. The National Rifle Association vowed to file a lawsuit to stop it.

Chief NRA lobbyist Chris W. Cox said the regulation is illegal, and that his organization would go to court as soon as the first firearms dealers receive written instructions from the ATF.

“This is just another attempt by the president and this administration to pursue their gun-control agenda,” Cox told the Houston Chronicle. “They do not have the authority by law to do this and therefore it is illegal.”

A local gun dealer said the rule would not stop cartels, but makes his job more time-consuming and hassles law-abiding customers.

“I do not think it helps nabbing anyone at all,” said Jim Pruett, owner of Jim Pruett’s Guns and Ammo.

Additionally, Pruett said he is concerned the requirement amounts to a back-door way for the government to compile a list of who has rifles and where they live.

The NRA has promised to fight the new rules in court. (Official logo)

“I think we all object to the government knowing we have a particular gun,” he said. “It is something to be feared that the government knows what weapons you own. That is not part of the Constitution.”

The ATF said the names of gun purchasers will be kept for two years, provided they are not drawn into a weapons investigation. An ATF official said having the list allows investigators to quickly figure out who is making multiple purchases of weapons prized by cartels and determine if they need further scrutiny.

“Not only will it make it more difficult for these traffickers to acquire firearms, it will also make it easier for ATF and law enforcement to identify the traffickers,” the official said.

Up until now, the ATF has depended on either dealers voluntarily reporting the names of suspicious customers or flagging names during annual records inspections.

Mexican officials long have complained about gangsters obtaining weapons from the United States. Mexico’s national security spokesman, Alejandro Poire, said in a statement that the Mexican government welcomes the new regulations as the two countries “improve the security conditions of communities on both sides of the border.”

President Felipe Calderon claimed in a speech last month in California that 85 percent of the more than 100,000 weapons captured from gangsters in the past five years came from U.S. gun dealers.

“I blame the North American weapons industry for thousands of deaths occurring in Mexico,” Calderon said.

Dozens of guns purchased in Houston have been traced to kidnappings and murders in Mexico. In one recent U.S. federal investigation of 70 weapons bought here by arms traffickers, 36 were used in homicides. The dead include 19 cartel members and 17 civilians or law officers.

A Chronicle/Hearst Newspapers survey in May of 44 gun prosecutions in Texas, Arizona, California, Nevada, Oklahoma and New Mexico pinpointed a total of 1,600 U.S.-purchased guns by brand name that were recovered in Mexico or intercepted en route.

A recently captured leader of the Zetas, the cartel based in cities bordering South Texas, told interrogators his gunmen get all of their guns from north of the Rio Grande.